WorksheetsPIPE ELEMENTS 1.2
Total questions: 100
Worksheet time: 50mins
What is the main reason combined cycle plants are more efficient than steam-only plants?
They require no condenser
They have no moving parts
They recover waste heat from gas turbine exhaust
They use higher turbine inlet temperature
Which factor reduces combined cycle efficiency at high ambient temperature?
Lower cooling water temperature
Lower inlet air density reducing gas turbine output
Higher condenser vacuum
Increased HRSG efficiency
Which efficiency compares electrical output to fuel energy input?
Volumetric efficiency
Indicated thermal efficiency
Mechanical efficiency
Overall plant efficiency
What is the main purpose of an air preheater?
To increase condenser vacuum
To increase furnace temperature by heating combustion air
To lower fuel pressure
To reduce steam temperature
What is the function of a bypass stack in dual-shaft CCPP?
To vent GT exhaust directly when HRSG is out of service
To superheat steam
To cool feedwater
To reduce generator load
Which factor improves Rankine cycle efficiency?
Low turbine inlet temperature
High boiler pressure and low condenser pressure
High moisture content
Low feedwater temperature
What is the typical efficiency range of HRSG alone?
70-85%
50-60%
10-20%
90-95%
Which parameter is kept constant in Brayton cycle compression?
Entropy
Volume
Pressure
Temperature
Which efficiency is defined as Net Power Output / Fuel Input Heat?
Isentropic efficiency
Boiler efficiency
Plant thermal efficiency
Mechanical efficiency
What is the typical exhaust gas temperature from a gas turbine entering the HRSG?
800-1000°C
Above 1200°C
150-200°C
300-600°C
What is the preferred enclosure rating for outdoor gensets in harsh weather?
IP54 or higher (or NEMA equivalent)
IP20
IP00
IP10
What is compressor surge?
High efficiency state
Excessive cooling of blades
Normal stable operation
Reversal of flow in compressor
What is compressor stall?
Reversal of flow in compressor
High efficiency state
Excessive cooling of blades
Normal stable operation
What is the governing equation for convective mass transfer analogous to heat transfer?
Newton’s law
Fick’s law
Bernoulli’s equation
Fourier’s law
Which factor lowers combined cycle performance at part load?
All of the choices
Higher auxiliary consumption
Reduced GT efficiency
Reduced steam production
Which type of head includes elevation difference?
Pressure head
Static head
Gross head
Net head
What is the ratio of useful work output to total heat input in a heat engine?
Work ratio
Efficiency
Exergy
COP
Which auxiliary maintains boiler feedwater purity?
Condenser
Demineralization plant and deaerator
Superheater
Drum
What is the reason for installing exhaust rain caps on outdoor stacks?
To increase backpressure excessively
To increase noise
To prevent rainwater ingress
To reduce PF
Which system provides cooling water for condensers?
Circulating water system
Feedwater system
Lubrication system
Boiler drum
Which section of Rankine cycle improves by regeneration?
Feedwater heating
Condensation
Superheating
Expansion
Which type of fin is most commonly used in heat exchangers?
Pin fin
Straight fin
Perforated fin
Annular fin
Which part of combined cycle plant usually governs ramp rate?
Steam turbine
HRSG
Gas turbine
Diffuser
Which component extracts energy from hot gases to drive the compressor?
Power turbine
Gas generator turbine
Intercooler
Diffuser
Which device ensures boiler water does not overheat the furnace?
Blowdown valve
Fusible plug
Thermostat
Safety valve
Which instrument measures boiler steam pressure?
Tachometer
Flow meter
Manometer
Pressure gauge
Which component improves efficiency by preheating feedwater with bled steam?
Economizer
Superheater
Feedwater heater
Deaerator
Which turbine is installed for very low heads (2–10 m)?
Kaplan or bulb turbine
Impulse turbine
Pelton wheel
Francis turbine
Which cycle governs the topping cycle in combined cycle plants?
Rankine cycle
Camot cycle
Carnot cycle
Rankine cycle
Which turbine is a mixed flow reaction turbine?
Pelton wheel
Impulse turbine
Francis turbine
Kaplan turbine
What is the function of variable inlet guide vanes in compressors?
To lower exhaust pressure
To control airflow and prevent surge
To regulate turbine speed
To reduce blade erosion
What is the function of labyrinth seals in turbines?
To reduce noise
To reduce leakage of cooling or working gas
To improve regeneration
To increase combustion efficiency
Which boiler efficiency test calculates various heat losses?
Direct method and indirect method
Direct method
ASME method
Indirect method
Which type of condenser is used in most large plants?
Jet condenser
Surface condenser
Dry condenser
Evaporative condenser
Which factor increases specific power output of gas turbines?
Low pressure ratio
High exhaust pressure
High lube oil flow
High turbine inlet temperature
Which type of HRSG has separate sections for HP, IP, and LP steam?
Triple-pressure HRSG
Single-pressure HRSG
Dual-pressure HRSG
Once-through HRSG
The spontaneous ignition of oil-soaked rags is primarily due to:
High ash content
High specific gravity
Low flash point
Oxidation releasing heat
What is the purpose of a crankcase explosion relief valve?
To prevent crankcase explosion damage
To increase compression
To control speed
To release intake pressure
Which method increases plant capacity factor?
High outages
Low load factor
Poor scheduling
Better maintenance and high availability
Which alarm indicates alternator overexcitation?
Low PF alarm
Low field current
High field current/overtemperature
Low voltage
What is the function of turbine shrouds?
To increase axial velocity
To lower emissions
To cool turbine blades
To reduce tip leakage and improve efficiency
Which dam type uses mass to resist water pressure?
Arch dam
Rock-fill dam
Buttress dam
Gravity dam
Which factor determines HRSG gas-side pressure drop?
Fuel type
Generator frequency
Tube geometry and gas velocity
Condenser vacuum
Which type of condenser is used in most large plants?
Dry condenser
Evaporative condenser
Surface condenser
Jet condenser
For safe storage of liquid fuels, the container should be:
Heated continuously
Well-sealed and vented to prevent pressure buildup
Unvented
Transparent
What is the typical range of net plant efficiency for combined cycle power plants?
35–45%
70–80%
20–25%
50–60%
Which fuel property affects boiler design?
Fuel price only
Calorific value, ash content, and moisture
Fuel availability only
Fuel density only
What is the thermal efficiency trend with increasing pressure ratio in Brayton cycle?
Always decreases
Increases initially, then decreases
Always increases
Independent of pressure ratio
Which auxiliary increases boiler efficiency by heating combustion air?
Air preheater
Economizer
Superheater
Deaerator
Which type of combustion chamber has lowest pressure loss?
Tubular
Can
Can-annular
Annular
Which turbine stage extracts energy to drive the compressor?
Free turbine
Power turbine
Gas generator turbine
Diffuser
What is the main advantage of axial-flow compressors over centrifugal types?
Higher pressure rise
Lower cost
Lower weight and higher efficiency at large capacities
Simpler design
Which combustion chamber type is commonly used in stationary gas turbines?
Tubular
Can-annular
Annular
Can
Smoke point of kerosene measures
Flash point
Calorific value
Sooting tendency
Auto-ignition temperature
Which device is used to remove scale and sludge from boiler?
Fusible plug
Economizer
Blowdown valve
Safety valve
Which type of head loss occurs in penstock bends?
Gross head
Static head
Major head loss
Minor head loss
What is the function of condenser circulating water cooling tower?
To increase GT output
To condense HRSG steam
To remove oxygen
To dissipate heat to atmosphere
Which method of blade cooling is most widely used?
Water cooling
Oil cooling
Steam cooling
Air cooling
Which cycle efficiency increases with reheating and regeneration?
Brayton cycle
Otto cycle
Rankine cycle
Diesel cycle
Which cycle modification requires feedwater heaters?
Intercooling
Reheating
Exhaust bypass
Regeneration
What is the function of steam bypass system in CCPP?
To reduce emissions
To divert steam directly to condenser during turbine trip
To increase HRSG efficiency
To cool condenser water
Which device measures turbine inlet temperature?
Flowmeter
Tachometer
Thermocouple array
Pressure gauge
Which number indicates tendency to knock in gas turbines?
Flash point
Octane number
Cetane number
None, since knock is rare in continuous combustion
Which factor reduces condenser performance?
Clean tubes
A high cooling water inlet temperature
Low dissolved oxygen
Proper sealing
Which system removes non-condensable gases from condenser?
Blowdown valve
Feedwater pump
Fusible plug
Air extraction pump or steam ejector
Which part of CCPP requires maximum water treatment?
Gas turbine
Generator cooling
Condenser cooling
Steam cycle
What indicates alternator unbalance?
Unequal phase currents/voltages under balanced load
Balanced phase currents
Correct PF
Stable temperature
Which factor governs Kaplan turbine blade adjustment?
Constant head only
Generator excitation
Load and flow variations
Reservoir level only
Which cycle modification increases both efficiency and power output?
Regeneration and reheating
Reheating only
Intercooling only
Bypass
Which gas is colorless, odorless, and highly poisonous?
SO2
CH4
CO2
CO
Which instrument displays generator real power?
Ammeter
Wattmeter
Synchronoscope
Voltmeter
Which efficiency is defined as gross generation divided by heat input?
Relative efficiency
Net efficiency
Polytropic efficiency
Gross efficiency
Which factor affects cavitation index?
Generator losses
Fuel flow
Excitation
Net positive suction head (NPSH)
Which system provides redundancy in case of lube oil pump failure?
Emergency DC lube oil pump
Jacking oil system
Feedwater heater
Steam bypass system
Which cause results in low insulation resistance after flooding?
Moisture ingress
High PF
Good ventilation
Dry windings
The calorific value of propane (LHV) is about
30 MJ/kg
20 MJ/kg
46 MJ/kg
55 MJ/kg
Which method reduces auxiliary power consumption in CCPP?
Oversizing HRSG
High efficiency pumps, fans, and variable frequency drives
Using low pressure turbines
Increasing condenser pressure
Which boiler mountings are legally required?
Economizer and air preheater
Chimney
Safety valve, water gauge, pressure gauge
Superheater
Which measurement indicates compressor fouling?
Constant mass flow
Increased exhaust temperature and reduced pressure ratio
Higher efficiency
Reduced consumption
For natural gas firing, the excess air requirement is generally:
30-40%
0-5%
10-15%
50-60%
Which factor limits the maximum pressure ratio in a single-stage centrifugal compressor?
Diffuser design
Blade material
Shaft diameter
Impeller speed and Mach number
Which property indicates the rate at which a material conducts heat relative to its heat capacity?
Thermal conductivity
Specific heat
Density
Thermal diffusivity
What is the preferred load range for best SFC in many diesels?
60-80%
0-20%
90-100%
25-50%
Which property defines steam enthalpy at turbine exit?
Heat rate
Fuel calorific value
Pressure ratio
Dryness fraction
What is the immediate risk of running below minimum lube oil level?
High power factor
Bearing failure and seizure
Low frequency
High voltage
Which part of boiler absorbs radiant heat from the furnace?
Air preheater
Superheater
Waterwall tubes
Economizer
Which factor governs Kaplan turbine blade adjustment?
Reservoir level only
Constant head only
Load and flow variations
Generator excitation
What is the key advantage of triple-pressure HRSG design?
Smaller size
Reduced pressure losses
Higher efficiency and steam generation
Lower cost
Which factor defines hydro plant firm capacity?
Average load
Maximum installed capacity
Reservoir capacity
Guaranteed power output during minimum flow
Which efficiency is improved with intercooling?
Isothermal compression efficiency
Thermal
Regenerative
Mechanical
Which cooling configuration minimizes raw water fouling?
Open-loop direct seawater
Air-cooled radiator only
Spray pond
Closed-loop jacket water with plate cooler
What is the usual power factor of gas turbine generators?
0.5
1.0
0.8-0.9
0.7
Which cycle modification reduces turbine exhaust wetness?
Reheating
Intercooling
Draft control
Regeneration
The heating value of a gaseous fuel is normally expressed in:
kJ/kg
kJ/m^3 at standard conditions
kg/mol
% by weight
Which device stores steam to handle load fluctuations?
Superheater
Steam drum
Economizer
Turbine
What is the function of an attemperator in HRSG?
To increase turbine efficiency
To control superheated steam temperature
To add oxygen to feedwater
To regulate condenser vacuum
Which factor governs HRSG pinch point?
Condenser pressure
Difference between exhaust gas and saturated steam temperature
Turbine speed
Fuel type
Which factor improves plant reliability?
Scaling
Poor lubrication
High outages
Preventive maintenance and condition monitoring
Which type of feedwater control is best for large rapid load changes?
Single-element control
Two-element control
Manual control
Three-element control
What is the purpose of a cooling tower in a steam power plant?
To increase turbine speed
To superheat steam
To reduce boiler pressure
To cool condenser water
